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Climate in Context: August 18, 2010

Arctic Ice Update

Every winter, the surface of the Arctic Ocean freezes pretty much solid (or, more precisely, the surface freezes), Every summer, some of that ice melts to expose open water — and for the past several decades, the amount of open water in late summer has gotten gradually, though somewhat erratically, larger. The biggest meltback was in 2007, and since then, the summer ice has rebounded slightly. It hasn’t been much of a rebound, though. During the summers of 2008 and 2009, the area covered by ice in mid-September (the annual low point) was a little more than in 2007, although still significantly less than the 1979-2000 average.

Now the National Snow and Ice Data Center (NSIDC) has come in with its latest report: as of two days ago, the ice at the top of the world covered about 5.95 million square kilometers of sea — about a half-million more than at this point in the summer of 2007, but about one and a half million less than what should be there at this point based on the 1979-2000 average.

On the chart below, the black line shows the long-term average; the dotted line is the record melt year of 2007, and the blue line represents this year so far. You can also see that only 2007 and 2008 had less ice than we’ve got this year. It’s the kind of “rebound” you’d expect if you dropped a half-deflated basketball on the gym floor.

Arctic sea ice extent during the 2007-2010 melt seasons (2010 trend so far is in blue), compared to 1979-2000 average conditions. Credit: National Snow and Ice Data Center.

All of this matters — and not just to the polar bears who do most of their hunting out on the sea ice. When the ice disappears, so does its ability to reflect sunlight out into space. The water below starts absorbing the light, heats up, and in turn heats the atmosphere, amplifying global warming (the phenomenon is known as “arctic amplification”). The fact that there’s a little more ice this year than in 2007 doesn’t help counteract that much.

And in fact, it’s not absolutely certain how this year will end up. One factor that affects ice extent is the weather during the short Arctic spring and summer: one reason ice plummeted in 2007 was that prevailing winds blew lots of ice out into the North Atlantic. This month, says the NSIDC, the winds are pushing ice northward, which tends to “reduce the total ice extent, especially since much of the ice pack is spread out.”

You think this is hot?

World leaders, along with many climate scientists, have agreed that the world should reduce greenhouse-gas emissions and take other actions to limit global average temperatures to no more than 2 degrees Celsius above pre-industrial levels (that’s one of the primary goals of the non-binding Copenhagen Accord that came out of the tumultuous United Nations-sponsored negotiations in Denmark last December). Let the world get any hotter, they say, and the consequences — including sea-level rise, extreme weather events and other disasters — could be devastating.

Whether or not we’ll actually hit that mark is open to some pretty serious debate, since it would require steep emissions cuts beginning in the next few years, but even if we do limit climate change to 2 C or below, the consequences could still be pretty damaging. A new paper scheduled for publication in the American Geophysical Union (AGU) journal Geophysical Research Letters points out that an overall two-degree rise won’t be spread evenly across the planet — and that some areas will feel a lot more heat than that, particularly in the form of extreme events. “…even if climate change is limited to 2 degrees Celsius on average,” says a related blog post on the AGU’s Geospace blog, “some parts of the world will likely be hit with scorching heat waves unlike any they suffer today.” Given that we’ve been experiencing some pretty awful heat waves lately, that’s not an encouraging prediction.

Maybe it's just sunspots after all

A candidate for Wisconsin’s September Republican senatorial primary has made it official: climate change is not due to human activity. "It's far more likely that it's just sunspot activity or just something in the geologic eons of time," said Oshkosh businessman Ron Johnson in a speech on Monday, according to an article in the online edition of the Milwaukee Journal-Sentinel. “Johnson, in an interview last month,” the story continues, “described believers in manmade causes of climate change as "crazy" and the theory as "lunacy."

Actual climate scientists disagree, of course. But scientists do have good news for those who more generally reject the notion that we paltry humans can do any serious damage to the environment. A new study out of Durham University, in the U.K., argues that wooly mammoths were not driven to extinction by hunting, as one leading theory has long maintained. Instead, say Brian Huntley and his colleagues, a computer simulation of vegetation across the Northern Hemisphere during the past 42,000 years shows that it was the disappearance of the mammoths’ grassland habitat that caused their decline.

The cause of the decline: climate change at the end of the most recent Ice Age. That wasn’t caused by humans either; we didn’t start burning fossil fuels in quantity until about 250 years ago. But as actual scientists would also point out, the fact that something can be caused by natural forces doesn’t mean it can’t also be triggered by human activity. After all, forest fires were ignited naturally, by lightning, for millions of years before humans invented matches.